I wouldn't recommend displaying your cels unless 
they are protected behind UV glass. Even then, 
you're taking a chance of fading. I suppose you 
can keep them in a cel bag and somehow attach 
them to the wall, but just remember, you're 
exposing the cel with no protection from light. 
Framed or no, make sure it's displayed in an area 
that receives little direct sunlight and isn't 
going to be exposed to moisture. (keep it away 
from the bathroom...believe it or not, those 
steaming hot showers can damage your cels!) 
Personally, unless you're going to frame them 
using the UV glass, non-acetate matte, and the 
proper "set-up" technique (ie using mattes to 
raise cel off the background, using protective 
layers etc)...I personally wouldn't think of 
taking them out of my cel book. Even using all 
these precautions, I only display the cels that 
are a least marginally replaceable. 

Hope that helped!